Keywords

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia. It is often treated using catheter ablation, which aims to isolate arrhythmogenic regions by delivering localized energy. Whereas an insufficient energy delivery can lead to AF recurrence, excessive power can cause potentially lethal complications. Knowledge of atrial wall thickness can help select an optimal amount of energy, but clinical imaging does not currently provide atrial wall thickness data for patients. Even ex-vivo studies have only measured the thickness of the atrial wall in discrete locations using CT or post-mortem samples.

In this study, we apply black-blood MR imaging to reconstruct both epi- and endocardial surfaces of the entire atria and compute wall thickness maps in healthy volunteers. To our knowledge, this is the first study to provide a complete 3D map of the wall thickness of both right and left atria.

Manual segmentation of the epi- and endocardial surfaces from the images was performed using ITK-SNAP. Triangular meshes of each of the surfaces were generated using Matlab and smoothed with a curvature flow operator (mean internode distance: 0.56 mm). Wall thickness was then computed by: A) measuring the distance between each node in the endocardial surface and its nearest neighbour in the epicardial surface; B) repeating procedure A in reverse for each node in the epicardial wall and C) averaging the outcomes of procedures A and B.

Results

Blood signal was strongly attenuated in relation to the myocardium, allowing the reconstruction of both the epi- and endocardial surfaces from the PSIR images (Fig. 1). The measured atrial wall thickness for each subject is mapped onto the epicardial surface and shown in Fig. 2. Wall thickness was on average 3.01 ± 1.09 mm (range: 2.80 ± 1.05 to 3.32 ± 1.16 mm), in good agreement with post-mortem data. The distinctive atrial bundle of the crista terminalis is clearly visible as a ridge with increased thickness and the pulmonary vein sleeves are thinner than other regions of the atria.

Conclusions

We developed a protocol that allows us to obtain 3D high-resolution bi-atrial wall thickness maps in healthy volunteers. Additional data is being acquired to create an atrial wall thickness atlas of healthy subjects. Future work includes acquiring data from AF patients to quantify the atrial wall changes caused by disease and provide a tool to aid catheter ablation treatments.

Funding

British Heart Foundation and KCL Centre of Excellence in Medical Engineering.

Copyright information

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.